1. Field
The following description relates to a capacitive humidity sensor, and to capacitive humidity sensor that minimizes a humidity sensitive area by increasing a variation of capacitance according to a humidity change to improve sensitivity.
2. Description of Related Art
A humidity sensor is a sensor that detects a level of humidity based on an electrical signal that changes its value with a change of humidity. A humidity sensor may accurately sense the humidity level by determining a change in an electrical property of a humidity sensitive material due to moisture.
Humidity sensors may be divided into resistive humidity sensors and capacitive humidity sensors. Humidity sensors are widely used to maintain automobiles, medical devices, air purification systems, automatic cooling/heating systems, home appliances, mobile devices and the like in an optimal state.
A resistive humidity sensor measures humidity based on a change in resistance that is changed by humidity. Resistive humidity sensors are widely used because resistance humidity sensors tend to be price competitive in comparison to capacitive humidity sensors.
However, recently, capacitive humidity sensors are manufactured on a semiconductor substrate in a one-chip form. Accordingly, it may be possible to obtain capacitive humidity sensors that are more price competitive than resistive humidity sensors. As a result, the use of capacitive humidity sensors is increasing.
Further, capacitive humidity sensors may exhibit higher reliability, and may exhibit more linear sensor features and low influences due to a temperature, in comparison to resistive humidity sensors. A capacitive humidity sensor may operate as a capacitor type device having a humidity sensitive material such as polymer or ceramic absorbs moisture, which has permittivity that is changed in the presence of moisture. That is, a humidity sensitive layer for sensing humidity may be present inside the device, and the permittivity of the humidity sensitive layer may change when moisture is introduced through the humidity sensitive layer. As a result, the capacitance is changed, and the capacitance may be determined to determine a level of humidity.
An example of a capacitive humidity sensor for sensing humidity is disclosed in U.S. Pat. No. 6,690,569 (Capacitive Sensor).
Referring to U.S. Pat. No. 6,690,569, the humidity sensitive material is filled between different electrodes to form a measuring layer.
Therefore, when a potential difference is applied to both ends of the electrode, an electric field is formed around the electrode. For instance, the largest electric field is formed in a space between electrodes having different potentials and facing each other.
However, in the capacitive humidity sensor, since moisture cannot penetrate a substrate below an electrode, a variation of permittivity is not changed. Therefore, a variation of the capacitance is limited.
Further, in a device in which a single conductive layer is used as the electrode, an electrode height is limited depending on a process capacity. Then, a dimension in which the electrodes overlap with each other decreases, and as a result, a variation of the capacitance depending on a humidity change is limited.
As such, as the variation of the capacitance is limited, sensitivity is reduced, deteriorating the sensing characteristics and response characteristics of the capacitive humidity sensor.
Accordingly, in order to maintain the sensitivity of the capacitive humidity sensor, an area occupied by a dielectric material needs to be secured to some degree. The dielectric material maybe a humidity sensitive material having a property in which permittivity is changed depending on moisture content. However, in order to increase the area occupied by the dielectric material, the size of the sensor cannot be reduced more than the area needed for the dielectric material. As a result, devices and products in which the sensor may be installed are limited due to the size of the sensor.